Evolution des leucocytes et neutrophiles sanguins et de la myéloperoxidase plasmatique durant la période péri opératoire de chevaux opérés pour coliques.

Background: Despite the recent advances in this area, colic remains a major cause of morbidity and death in horses. Neutrophilic activation and degranulation may play a key role in the postoperative complications. Activated neutrophils release enzymes like proteases and myeloperoxidase (MPO). MPO concentrations in plasma and tissue are considered as a marker of neutrophil activation. (McConnico et al. 1999; Hoy et al. 2002). When freed in the tissue, active MPO is able to oxidize, nitrate and chlorate most organic molecules (Klebanoff 2005). Objectives: The aim of this study was 1) to determine the time trends of blood leukocyte and neutrophil counts as well as of plasmatic MPO concentrations in the perioperative period of horses undergoing colic surgery and 2) to relate these time trends to the location of the pathology, the severity of postoperative complications and to the outcome of the patients. Methods: Fifty two horses undergoing colic surgery at the Equine Teaching Hospital of the University of Liege were included in this study. The location of the predominant lesion of the intestine, the severity of the postoperative complications and the outcome were recorded for each horse. Total leukocyte and neutrophil counts were performed in all of the horses while plasmatic myeloperoxidase levels were determined in 16 of them. The blood samplings were realized before and during the surgery (after correction of the intestinal lesion), during the recovery and every 4 hours during the first 4 days (from day 0 until day 4) and then every 12 hours until day 6 (150th hour after the first blood sampling) or until euthanasia. Hematologic analyses were performed at the time of sampling by use of the Medonic CA 530 (Menarini, Zaventem, Belgium). The blood was then centrifuged and the plasma was aliquoted and frozen at -20° C until assayed. MPO was assayed with a specific enzyme-linked immunosorbent assay (Equine MPO-ELISA kit, BiopTis, Liège, Belgium). A mixed model was used to analyze the time trends of leukocytes, neutrophils and MPO. All computations were done with the SAS (Statistical Analysis System) procedure Proc Mixed, with Satterthwaite degrees of freedom. The significance level was set at p=0.05. Results: The main pathology was found in the large intestine in 30 horses (58%) and the small intestine in 22 horses (42%). Forty horses (77%) survived to discharge from the clinic. Twelve horses were euthanized during the postoperative period. Their survival time varied from 0.5 day to 20 days with a mean of 7.8 days. Twenty-two horses (42%) showed none or mild complications, 12 horses (23%) showed moderate complications and 18 horses (35%) suffered from severe complications. Time trends for leukocytes and neutrophils were similar to each other (p= 0.7205) and significantly different (p< 0.0001) from the MPO time trend, which increased during the first hours, while the neutrophil time trend decreased immediately after the admission. The time trend of neutrophils was higher in large intestinal than in small intestinal pathologies and the time trend of MPO was lower in large intestinal than in small intestinal pathologies. The time trends of neutrophils were significantly different between the degrees of complications (no/mild vs moderate vs severe). For the first part of the curve, the more severe the complication, the lower is the time trend. The time trend of MPO was lower in survivors. The time trend of neutrophils in survivors was higher during the first 4 days thereafter it becomes lower than in non survivors. Conclusions: These results confirm that neutrophil counts and MPO levels undergo timely changes and that they are related to the severity of the inflammatory reaction in surgical colic cases. Knowing the kinetics of these parameters is an essential step to further determine cut-off values (with a larger group of horses) for the prognosis of horses after colic surgery. References Hoy, A., Leininger-Muller, B., Kutter, D., Siest, G. and Visvikis, S. (2002) Growing significance of myeloperoxidase in non-infectious diseases. Clin. Chem. Lab. Med. 40, 2-8. Klebanoff, S.J. (2005) Myeloperoxidase: friend and foe. J. Leukoc. Biol. 77, 598-625. McConnico, R.S., Weinstock, D., Poston, M.E. and Roberts, M.C. (1999) Myeloperoxidase activity of the large intestine in an equine model of acute colitis. Am. J. Vet. Res. 60, 807-813